Employee Benefits - Components of Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
U.K.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0
Interest cost	16	22
Expected return on plan assets, net of administration expenses	(34)	(39)
Amortization of prior-service cost	1	0
Amortization of net actuarial loss	8	7
Total net periodic (benefit) cost	(9)	(10)
Other
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	3	4
Expected return on plan assets, net of administration expenses	(8)	(8)
Amortization of prior-service cost	0	0
Amortization of net actuarial loss	4	3
Total net periodic (benefit) cost	(1)	(1)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	14	21
Expected return on plan assets, net of administration expenses	(32)	(33)
Amortization of prior-service cost	0	0
Amortization of net actuarial loss	19	17
Total net periodic (benefit) cost	$ 1	$ 5